DESCRIPTION (Investigator's Abstract): Fever is a coordinated autonomic, endocrine and behavioral response that is orchestrated by the hypothalamus during immune stimulation. It is thought that fever is caused by circulating cytokines such as interleukin-1b (IL-1) acting on the organum vasculosum of the lamina terminalis (OVLT), a portion of the preoptic area that is outside the blood-brain barrier. The mechanisms by which the OVLT activates hypothalamic responses resulting in fever are not known, although it appears to involve prostaglandin E2 (PGE2) as an obligatory messenger. PGE2 may act on thermosensitive ionic currents of thermoregulatory neurons in the preoptic area, which may produce fever by activating autonomic and endocrine responses via the paraventricular nucleus of the hypothalamus. However, critical evidence is missing to support this theory and to determine the exact mechanisms for PGE2 action during fever. The experiments will test whether the OVLT is the key site of prostaglandin production in IL-1 fever by using a new preparation that we have developed for testing fever responses following microinjection into the OVLT and adjacent areas of ketorolac, a recently developed water-soluble inhibitor of cyclooxygenase. Second, the pattern of activation of neurons in the brain during IL-1 fever (as evidenced by Fos expression), and the suppression of this activation pattern by blockade of prostaglandin production by ketorolac injection in the OVLT, will be examined. Third, the connections with the paraventricular nucleus of the hypothalamus of the preoptic neurons that are activated by IL-1 fever, and the neurotransmitters they may contain, will be identified using a combination of Fos-immunocytochemistry with retrograde labeling with cholera toxin B subunit, and either immunocytochemistry or in situ hybridization for atrial natriuretic peptide, galanin, enkephalin, substance P or tumor necrosis factor a. Finally, the cellular mechanisms by which thermoregulatory neurons in the preoptic area respond to PGE2 will be studied by performing intracellular recordings using whole cell patch clamp methods, directed at thermosensitive neurons that are retrogradely labeled by injections of fluorescent microspheres into the paraventricular nucleus of the hypothalamus. These experiments should provide a basis for understanding the mechanisms by which circulating cytokines activate neuronal networks involved in fever and CNS responses to immune stimulation.